Combine -b and -dump. Using -b will quickly bypass the preceding frames. Just don't set -b and -dump to the same value; that may not work (same with -b and -e).

Thanks, I know these two flag, why I didn't think of it before.

After, I do some test, it seems both with -b or without -b give u similar run time. But I think with -b may give you a bit boost, since it skipping the frame not reading.

Anyway, -e flag is not require, since it will stop once it reach the -dump frame.

Justin Lemkul i want to ask you how to extract a single number of frames from eigenvec.trr ? i have used trjconv -f eigenvec.trr -o vec1.trr -b 66 -e 67. that b value i have taken it from eigenval.xvg file. but when i proceed for extracting second vec.trr by using same command but -b is now 18 and -e 19 as the second value in eigenval.xvg for the second frame is that but i have got an error that :

Will write trr: Trajectory in portable xdr format

trn version: GMX_trn_file (single precision)

Last frame 11 time 18.519

WARNING no output, last frame read at t=2.08183

the values in eigenval.xvg are:

@ title "Eigenvalues of the covariance matrix"

@ xaxis label "Eigenvector index"

@ yaxis label "(nm\S2\N)"

@TYPE xy

1 66.5293

2 18.5191

3 14.8288

4 12.3237

5 9.53107

6 5.85064

7 4.29942

8 2.62136

9 2.35924

10 2.08183

i want to extract these each values in seperate vec.trr files. how can i extract them ?

Ayesha Kanwal trjconv is not designed for this purpose. Check options in gmx anaeig.